Powerful, low power processors allow for new functions to be added to old devices and for new devices to be created. Some of these functions relate to audio processing. Some tablet computers and smart phones are available with four separate microphones. These use significant audio processing to improve the audio. The multiple microphones may be used to provide audio recordings with a spatial aspect and the audio processing may be used to provide lower noise for monaural and multiple dimension recordings. Many devices offer voice control by capturing spoken statements from the user and either sending the captured audio to a remote server or processing the statements locally.
Multiple microphones are being added to wearable devices so that watches, helmets, glasses, and other worn apparel and apparatus may be used for recording, for communicating wirelessly with others in other locations, and for controlling devices using voice command. Hands free devices are being developed for training, maintenance, search and rescue and also for playing games either alone using voice commands or with multiple players using voice commands and conversation through a network.
For outdoor and industrial environments, wind can be a significant part of the audio field surrounding a microphone. The wind produces a flow of air that can cause a sustained sound pressure level (SPL) on the diaphragm of a microphone. Typically wind is also turbulent and inconsistent causing an irregular high level of SPL over time. Even on a calm day, when a user is bicycling, skiing, or motoring, wind may interfere with speech from the user or from others.
Wind flowing over a microphone will induce significant amounts of low frequency noise and can also introduce significant distortion. This is a problem for various types of voice transmission and sound recording systems. It is also a problem for digital speech encoding systems (CODECs), DSP (Digital Signal Processing) devices and other types of solutions inside communication devices. A DSP can provide significant enhancements to an audio signal for transmission, recording, or for application to an automatic speech recognition (ASR) system. These allow for better sounding audio or more easily understood voice. ASR requires a baseline level of quality over ambient noise in order to function reliably under adverse conditions. In particularly noisy and windy environments an ASR system may be unable to recognize many spoken statements.
The wind noise may be avoided by detecting vibrations on the user instead of vibrations carried as compression waves through the air. Bone conduction microphones sense vibrations in the skull, or nose to receive sound. These can be integrated into earpieces or headwear but require careful fitting to ensure physical acoustic coupling to the body. Throat microphones sense vibration through the neck caused by speaking. These types of microphones require physical contact with the speaker. Other speakers or ambient sounds cannot be suitably detected. In addition, the sensed vibrations do not include the full spectrum of the speech so that the sound is not suitable for recording or conversation and may be difficult to use in ASR.